Fiber optic communication links are an integral part of many computer systems. Since it is quite expensive to construct new fiber optic lines, various approaches have been devised to increase system capacity. These approaches include optical wavelength division multiplexing (WDM), dense wavelength division multiplexing (DWDM), coarse wavelength division multiplexing (CWDM) and, for certain data formats, time division multiplexing (TDM).
In a WDM or DWDM system, multiple optical channels are carried over a single optical fiber, each channel being assigned a particular optical wavelength. By using a single, existing optical fiber to carry multiple channels, DWDM has been found to be an efficient approach for increasing the capacity of data communication systems.
Each channel in a current DWDM system can carry data at speeds up to 10 Gbit/s. This works well for data that is being transmitted at such speeds, however, it is obviously inefficient to use a channel capable of 10 Gbit/s to transmit a signal at a substantially lower data rate.
TDM modules have been employed, for certain data formats, in an attempt to avoid such inefficiency. At the transmitting end of a TDM system, an electronic switch (multiplexing unit) picks up signals from multiple input channels, in a predetermined “channel-by-channel” order. A resulting multiplexed signal, which combines such input signals, is constructed and forms the “output” or transmitting end of the TDM system. The multiplexed signal is distributed to receiving terminal equipment as the output of the transmitting end of the module. TDM is discussed in detail in various publications, including a textbook by A. B. Carlson and D. G. Gisser entitled: Electrical Engineering Concepts and Applications, published by Addison-Wesley, N.Y. (1991), which is hereby incorporated herein by reference in its entirety.
Existing TDM modules typically work with a specific fixed data format. For example, modules have been designed to operate with the FDDI data format, while others work only in the Ethernet data format.